Antiparasite filter for radio receivers



Nov. 5, 1940. GABRILOVITCH 7 3 ANTIPARASITE FILTER FOR RADIO RECEIVERSFiled April 22, 1937 1 0a) freqa ency amp/zfier A H F Z Defec/ar CF-MF-D-A HP 17211611202" Leon/ d6 Gabrf/ovitch Patented Nov. 5, 1940 UNITEDSTATES ANTIPARASITE FILTER- FOR RADIO RECEIVERS Leonide Gabrilovitch,Paris, France Application April 22, 1937, Serial No. 138,310 In FranceApril 28, 1936 5 Claims.

The present invention is for the elimination of parasites in wirelesstelegraphy and telephony and utilizes two fundamental properties ofthese perturbations:

(1) Their very high damping which is the cause of the well-known factthat every parasite represents a sequence of waves of a very brief totalduration; and

2) The very irregular, non-sinusoidal shape assumed by the curves of thelow frequency currents produced by the parasites after detection.

These two properties, in a rather simple way separate the detectedparasites from the detected emissions. In fact, if at the reception, thecomplex of incoming waves passes through strongly damped circuits, or isamplified aperiodically, the sequences of waves, constituting theparasites, conserve their very brief total durations and become, afterdetection, very brief impulsions, the duration of which is considerablyinferior than that of the periods of the highest acoustic vibrations.

Let us now assume that we let pass the complex of low frequencycurrents, thus obtained, through a high-pass filter, the inferiorfrontier of which is situated above 6,000 cycles/second. Under thoseconditions, the emissions (i. e. music and speech) will not pass; onlythe impulsions produced by the detected parasites will pass.

If these impulsions, properly amplified, and directed, act thereafter onthe grid of an amplifier submitted to the action of the same complex ofincoming waves, this valve will be blocked every time when a parasitewill appear in the incoming complex. This blocking will have exactly thesame duration as the parasite. The amplification, thus controlled, letsthe high frequency oscillations pass during the intervals of timesituated between the perturbations. In such a way, the incoming complexis released from parasites. The very brief interruption of the emissionproduced by the blocking of the amplifier, disappears in the followingstages of amplification on account of the very reduced damping of theoscillating circuits placed there.

The figure of the drawing attached thereto, represents exclusively as anexample, one of the possible diagrams of the antiparasite devicedescribed above.

The upper row represents an ordinary radioreceiver formed by an aerialA, a high frequency amplifier (a semiaperiodical one) AHIF, a frequencychanger CF, a stage of intermediate frequency MF, a detector D, a lowfrequency amplifier .ABF and a loud speaker HP. This type of receivermay be replaced by any other type of receiver, either a superheterodyne, or a direct receiver, or any other type whatsoever. Especialcare however, should be taken to establish the first high frequencyamplification in such a way that it should not transform the stronglydamped, and consequently very brief, sequences of waves, constitutingthe parasites, into less damped sequences which, consequently would beof a relatively long duration.

The grid of this first high frequency amplifier (Ann) is submitted tothe action of the brief leaps of negative tension produced by thedetection of parasites effected in the auxiliary device represented inthe lower row of thefigure. The auxiliary device is influenced by thesame complex of incoming waves as the receiver drawn in the upper row,because both devices are connected to the same antenna A. The incomingcomplex passes first through the high frequency amplifier A'HF,constituted so that the strongly damped sequences of waves conserve thestrong damping and their very brief durations. For this purpose, eitheran aperiodic amplification (such as represented on the drawing), orsufliciently damped oscillating circuits, should be utilized. Afteramplification, the incoming complex is detected by the detector D, andthe system of low frequency currents, thus obtained, is led through ahigh pass filter FPH, the inferior frontier of which is situated abovethe musical frequencies, for instance, above 5,000 to 6,000cycles/second.

Thus, the filter FPH will stop all music and speech and will let passonly the very brief impulsions produced by the parasites after theirdetection. These impulsions will be amplified by the low frequencyamplifier A'BF and. led to the grid Ann in the proper manner, i. e., asnegative impulsions, either directly or through a rectifier Rw, orthrough push-pull rectifiers, in order to eliminate the impulsions ofopposite sign.

In this way, the valve AI-IF will be blocked every time a parasiteappears in the incoming complex, and this blocking has the same durationas that of the parasite in question. As to the interruptions produced bythese blockings, they are inevitably swept off under the action of thevarious oscillating circuits contained in the receiver, in view of theweak damping of these circuits and the very reduced duration of theinterruptions.

Having now particularly described and ascertained the nature of my saidinvention and in what manner the same is to be performed, I declare thatwhat I claim is:

1. In a wireless receiver a method for eliminating noise interferencecomprising first, detecting the whole plurality of incoming wavescomprising both the signals to be received and the interference, second,filtering the detected plurality of Waves to substantially absorb allwaves other than the interference, third amplifying the im pulses fromthe detected interference, fourth, amplifying the entire plurality ofincoming waves including the interference and permitting the detectedinterference to block the amplification of the interference coupled withthe signals to be received.

2. In a wireless receiver, the method of eliminating noise interferencewhich consists in, detecting the whole plurality of incoming wavescomprising the signals to be received and the interference, in filteringthe products of the detection to block out the signals and to transmitthe interference, and in amplifying the whole plurality of incomingwaves comprising the signals to be received and the interference andsimultaneously the filtered-out detected interference to permit thedetected interference to block and substantially to nullifyamplification of the interference coupled with the signal to bereceived.

3. In a wireless receiver the method of eliminating noise interferencewhich consists in detecting the whole plurality of incoming wavescomprising the signals to be received and the impressed interference inhigh-pass filtering the detected waves and interference with a lowerlimit substantially close to the upper audio-limit to absorb 'thedetected incoming signals while transmitting the higher frequencyinterference, and in amplifying the entire plurality of incoming wavescomprising the signals to be received and the impressed interference andsimultaneously the filtered detected interference to amplify onlydetected signals minus the disturbance by causing mutual blocking of thefiltered and the impressed disturbances.

4. In a wireless receiver, at least one high frequency amplifying stage,a detector stage for detecting the entire plurality of incoming wavescomprising the signals to be received and the interference, a filter forfiltering out and transmitting the detected interference, means forimpressing Onthe grid of the high frequency stage the entire pluralityof incoming waves comprising the signals to be received and theinterference, the output of said filter being connected to said grid toimpress said detected filtered-interference thereon, the incominginterferences and detected filtered interference coacting to nullifyeach other while said signal is amplified substantially minusinterference.

5. In a wireless receiver a high frequency amplifyin stage, anaudio-frequency detector stage, means for impressing the entireplurality of incoming waves comprised of the signals to be received andthe interference upon both of said stages, a filter having a lower limitsubstantially close to the upper audio frequency limit in operativeassociation with the detector stage and having an output of detectedinterference of higher frequency than said signals, means operativelycoupling the output of said filter to the high frequency stage toimpress the detected filtered interference upon the high frequency stagewith the entire plurality of incoming waves to block the high frequencystage against transmission of the interference.

LEONIDE GABRILOVITCH.

